This invention relates to an amorphous alloy of high magnetic permeability suitable for forming a video or audio magnetic head, a magnetic shielding device, a transformer and other magnetic devices.
Conventional magnetic materials of high magnetic permeability suitable for forming a magnetic head, a magnetic shielding device, a transformer, etc. include, for example, crystalline alloys of Fe-Si system, Fe-Ni system, Fe-Al system and Fe-Si-Al system. Certainly, these conventional magnetic materials are satisfactory to some extent, but leave room for further improvements in magnetic properties, workability, etc.
Fe-Si alloy, which is widely used for forming a core of transformer and motor, has a magnetic permeability of at most about 500.
Fe-Ni alloy known as permalloy, particularly, permalloy containing 78 atomic % of Ni has a high magnetic permeability, but is insufficient in hardness, giving rise to difficulty in wear resistance when used for forming a magnetic head. Incidentally, a general method of producing a magnetic head comprises laminating a magnetic material, followed by synthetic resin molding. What should be noted is that the molding step causes a marked reduction in magnetic permeability of the magnetic material.
Some of Fe-Al alloys and Fe-Al-Si alloys have a high magnetic permeability, but are brittle, giving rise to difficulty in workability.
Recently, excellent magnetic and mechanical properties have been found in amorphous alloys. Unlike an ordinary cyrstalline alloy, an amorphous alloy does not have a periodicity in crystal structure. Various methods of producing an amorphous alloy are known to the art including, for example, vapor deposition, electrodeposition, electroless plating, sputtering and liquid quenching method. In particular, the liquid quenching method permits producing a bulky amorphous alloy having a good mechanical strength, hardness and flexibility in constrast to a thin film of an amorphous alloy obtained by the other mehtods mentioned above. Certainly, the bulky amorphous alloy is suitable for forming a magnetic head, the core of a transformer, a magnetic shielding device, etc. But, an amorphous alloy obtained by quenching is generally low in magnetic permeability, rendering it necessary to further apply heat treatment for increasing the magnetic permeability.
It has also been found recently that an amorphous alloy of Co-Fe-Si-B system is substantially free from magnetostriction and is high in magnetic permeability where the atomic ratio of Co to Fe is about 94:6. However, the range of mixing ratios of the component metals which gives a high magnetic permeability to an obtainable alloy by quenching is very narrow rendering it unsatisfactory in reproducibility. Such an alloy is also insufficient in hardness and poor in temperature stability.
It should also be noted that a magnetic material is exposed to high temperatures in some cases in the manufacturing step of a magnetic device or during the use of the produced magnetic device. For example, a magnetic material is heated to as high as about 150.degree. C. in a step of producing a magnetic head. In such a case, it is important that the deterioration of magnetic properties such as magnetic permeability should be prevented as much as possible. However, the deterioration mentioned is so much in the conventional amorphous alloy as to render the alloy unsuitable for practical use.